The present invention relates to recording and reproducing system, method and format.
In a recording and reproducing system, such as a magnetic tape recording and reproducing system, management information such as tape management information and file management information is very effective for locating and identifying data. The tape management information generally includes record update information items such as date and time of recording, a serial number of recording equipment, the position of a most recent TOC (table of contents) and the total number of recorded files, and other information items about a tape as a whole such as a recording format of the tape and a tape label. The file management information comprises information (such as TOC information) to identify and locate data recorded on the tape.
There are two techniques for recording such management information.
(1) A collection of tape management information and file management information is recorded in a predetermined segment of a tape.
(2) A collection of tape management information and file management information is recorded in an IC memory in a tape cassette.
The above-mentioned first technique enables recording of a vast amount of tape management and file management information with little limitation on the type of data recorded on a tape, and the number of data files. However, the recording and reproducing system is required to record the tape management information and file management information before ejection of the tape. Movement (or search) to a tape position for the management information requires considerable time. In reproduction (or playback), the recording and reproducing system must read the tape management information and file management information on a tape, consuming time for search and reproduction. To facilitate searching, the management information is generally written in an area immediately following the beginning of a tape, and a loading/ejecting operation is always done at the beginning of the tape.
The above-mentioned second technique minimizes the time for searching, recording and reproducing with its capability of instantly storing and reading management information at the time of tape loading or ejecting. However, the IC memory is limited in storage capacity, and unable to handle a large number of files.
Recording and reproducing systems are widely used for data backup in computer systems. In various scientific and technical fields, the need for a high-speed, multi-channel data recorder capable of recording an enormous amount of data is increasing. For example, a computer system for recording, in a real time manner, measurement data such as data on vibration of a bridge, or data on noise/vibration of a motor vehicle, requires a device for backup of large volumes of data. As a data backup device, data recorders using a magnetic tape of long recording time, such as AIT (Advanced Intelligent Tape) tape or DDS (Digital Data Storage) tape based on DAT (Digital Audio Taperecorder) technology, have come into wide use. (AIT is a trademark of SONY corporation, and DDS is a registered trademark of SONY corporation.)
FIG. 7 shows a typical example of such a computer system in which at least one computer (a personal computer or a workstation) is connected with at least one magnetic tape data recorder. In the example of FIG. 7, a CPU 1 of a computer is connected through a host adapter (or input/output channel) 2 having a unified set of control rules (protocol), with a plurality of peripheral controllers 3. Each peripheral controller 3 is connected with one or more peripheral equipment units of a predetermined type (such as magnetic tape recorder units 4, magnetic disc units 5, or printer units 6).
SCSI (Small Computer System Interface) is an I/O interface standard applicable for connection between the host adapter 2 and the peripheral controllers 3. SCSI enables connection of peripheral controllers of various types to a SCSI bus. For example, the following are ten connectable device types in SCSI-2 (expanded version of SCSI-1).
(1) direct access device (such as magnetic disk drive) PA1 (2) sequential access device (such as magnetic tape drive) PA1 (3) printer device PA1 (4) processor device PA1 (5) write-once device (such as recordable optical disk drive) PA1 (6) CD-ROM device PA1 (7) scanner device PA1 (8) optical memory device (such as erasable/writable optical disk drive) PA1 (9) media changer device (such as library type device) PA1 (10) communication device PA1 a control section for retrieving data in the data sets or files by using effective management information. The control section employs, as the effective management information, the management information recorded in a first memory area when there exists a first condition for regarding readout of the management information from the first memory area as effective, and the management information recorded in a second memory area when there is a second condition for regarding readout of the management information from the second memory area as effective. The different memory areas may be areas in a memory in a cassette, a memory in a recorder and a record medium in the cassette, or may be different areas or separate areas on a record medium. PA1 a data recording section for recording data files on a record medium contained in a cassette, and for reproducing data of the data files in accordance with management information which is also recorded on the record medium; PA1 a memory access section for allowing access to a cassette memory build in the cassette, for recording management information into the cassette memory and for reading the management information from the cassette memory; PA1 a recorder memory for storing management information; and PA1 a control section for retrieving data from the record medium by using, as effective management information, the management information obtained from one of the cassette memory, the recorder memory and the record medium, the control section reading the management information from the cassette memory, employing the management information of the cassette memory as the effective management information if the management information of the cassette memory corresponds to the data files recorded on the record medium, reading the management information from the recorder memory if the management information of the cassette memory does not correspond to the data files recorded on the record medium, employing the management information of the recorder memory as the effective management information if the management information of the recorder memory is in agreement with the management information of the cassette memory, and reading, as the effective management information, the management information from the record medium in the cassette if the management information of the recorder memory is not in agreement with the management information of the cassette memory. PA1 a first step of reading management information recorded in a cassette memory built in the cassette loaded in a data recorder; PA1 a second step of examining if the management information of the cassette memory corresponds to the data files recorded on the record medium; PA1 a third step of employing the management information of the cassette memory as the effective management information if the management information of the cassette memory corresponds to the data files recorded on the record medium; PA1 a fourth step of reading management information recorded in a recorder memory built in the data recorder if the management information of the cassette memory does not correspond to the data files recorded on the record medium, PA1 a fifth step of examining if the management information of the recorder memory is in agreement with the management information of the cassette memory; PA1 a sixth step of employing the management information of the recorder memory as the effective management information if the management information of the recorder memory is in agreement with the management information of the cassette memory; PA1 a seventh step of reading the management information from the record medium in the cassette if the management information of the recorder memory is not in agreement with the management information of the cassette memory. PA1 a recording section for recording a sequence of data files on a record medium; and PA1 a control section for recording a sequence of file management information sets on the record medium, each of file management information sets being recorded after one of the data files, and comprising information about a table of contents for a unique one of the data files and the data files preceding the unique one of the data files. Each data file may be a collection of data obtained from the start to the end of a recording operation. PA1 a plurality of recording steps for recording a sequence of data files on the record medium and a sequence of file management information sets on the record medium, each of the recording steps comprising a first sub-step of recording one of the data files, and a second sub-step of recording one of the file management information sets corresponding to the data file recorded by the first sub-step, each of the file management information sets being recorded after a corresponding one of the data files, and comprising information about a table of contents for the corresponding one of the data files and the data files preceding the corresponding one of the data files.
A magnetic tape unit is often called streamer because of its capability of transferring data like a stream.
FIG. 8 shows, as an example, a format of a recording tape used in a conventional streamer. A magnetic tape TP has a record area reserved for recording management information such as TOC information (Table of Contents). In the example of FIG. 8, the record area for TOC is located immediately after the beginning of the tape BOT. The TOC information comprises various information items such as items shown in FIGS. 9, 10 and 11. From the TOC record area to an EOD area for recording EOD information indicating the end of data, near the end of the tape EOT, there are a plurality of data record areas each for recording a collection of data (or data file).
In transferring recorded data to a computer, the computer first reads the TOC information, and performs a high speed search for target data by using the TOC information, such as an information item indicating a position of a data file. For example, the information item indicating the position of a data file comprises information about a recording start position and a recording end position of the data file. With the TOC information, the tape recording and reproducing system can transfer data to a computer very rapidly by finding target data on a tape at a high speed comparable to a fast forward speed or a rewind speed, without the need for operating a FF (Fast Forward) key or a REW (Rewind) key of the tape recording system.
The conventional streamer is thus arranged to record TOC information only at a single position just after BOT (or at some other appropriate position) on a tape. This is reasonable in a way for transferring data streamingly to a computer.
When, however, a computer becomes unable to read the TOC information due to minor tape damage only in the TOC record area or some other abnormality, the ability of high speed search is readily lost notwithstanding the integrity of all the data files on a tape. In such a case, the computer must read out data items one by one from the beginning of a tape until target data is reached.